arrstack: fix sync-wave deadlock + config multi-attach

The active-active arrstack deploy (#383) was stuck: the app Deployments
(wave 0) can't become Healthy without their database, so ArgoCD never
advanced to wave 1 to create the shared Postgres cluster. And /config was
an RWO cephrbd PVC, so 3 replicas hit Multi-Attach.

- move DB infra ahead of the apps: VSS + backup ObjectStoreUser/Bucket
  wave -3, CNPG Cluster -2, Databases -1 (apps stay at default 0)
- switch each app's /config to emptyDir (per-pod, stateless; library is
  in Postgres, config is env-driven; MediaCover regenerates). Old RWO
  config PVCs orphan.

apps/base/arrstack/postgres/cnpg_backup.yaml

@@ -7,6 +7,9 @@ kind: ObjectStoreUser
 metadata:
   name: cnpg-arrstack-backup
   namespace: arrstack
+  annotations:
+    # S3 creds Secret must exist before the Cluster (wave -2) reconciles its backup.
+    argocd.argoproj.io/sync-wave: "-3"
 spec:
   displayName: "CNPG backup owner (arrstack)"
   uid: cnpg-arrstack-backup
@@ -19,6 +22,8 @@ kind: Bucket
 metadata:
   name: cnpg-arrstack
   namespace: arrstack
+  annotations:
+    argocd.argoproj.io/sync-wave: "-3"
 spec:
   placementTarget: ec
   bucketName: cnpg-arrstack